Interpretive Summary: Castor beans are an important agricultural crop, used to make castor oil, an industrial lubricant. Ricin is a highly toxic protein that remains in the solids after oil is extracted from castor beans. Ricin has been used for intentional poisoning, and there is a need for methods to detect ricin in food to ensure a safe food supply. Many tests for detecting foodborne toxins utilize antibody-based methodology. In this paper we describe the use of an advanced technology to characterize the binding of antibodies to ricin toxin and related molecules. This method is known as biolayer interferometry and uses disposable dip-and-read sensors that detect the shifting pattern of light in response to molecular binding. By characterizing toxin-binding antibodies in this way, we can expect to improve food immunodiagnostic methods.

Technical Abstract:
Two related agglutinins are present in the seeds of Ricinus communis (castor): ricin, a dichain ribosome-inactivating protein and Ricinus communis agglutinin-1 (RCA-1), a much less toxic hemagglutinin. Because ricin has been used for experimental cancer chemotherapy as well as for intentional poisoning, the immunochemical analysis of these agglutinins is of special interest. We used the technique of biolayer interferometry (BLI) to characterize the binding of monoclonal antibodies to the agglutinins. We used several types of sensor chemistries (amine-reactive, Fc-binding, and streptavidin-coated) to study the interactions. The results of the binding studies indicate that sensor surface chemistry affects the results. The kinetically determined dissociation constants agreed with the relative binding observed in ELISA, though binding to isolated B-chain was an exception. We conclude that BLI provides a convenient dip-and-read method to characterize antibodies useful for immunodiagnostic applications in food matrices.